This is addressed to the elucidation of the mechanism responsible for fluid transport across the corneal endothelium. Several aspects of this mechanism will be studied. The osmotic permeability of the endothelial cell membranes will be assessed with an automatic procedure and subsequent computer analysis of the data. The relationship between the rate of fluid transport and the electrical potential difference and resistance across the endothelial layer will also be studied. Physiological and pharmacological agents reported to block specific ionic permeation sites in cell membranes or to create additional sites for ions and water will be employed to test our existing model for the fluid transport mechanism. The intracellular electrical potential difference will be measured with microelectrodes and the effects on it of conditions which inhibit or stimulate fluid transport will be determined. A theoretical model for fluid transport will be expanded so as to be able to ascertain its validity from existing experimental information and predict the behavior of the system under varying experimental conditions. All the information will be integrated into the context of the working models referred to above.